The Simulation of Atmospheric Carbon Dioxide Doubling Impacts on Climatic Changes in Tabriz Using Geophysical Fluid Dynamics Laboratory(GFDL) General Circulation Model

General circulation models (GCMs) are mathematical models (i.e. computer simulations) of atmospheric and oceanic properties and processes that attempt to describe earth's climate system(The global climate system is a consequence of, and a link between, the atmosphere, oceans, the ice sheets (cryosphere), living organisms (biosphere) and the soils, sediments and rocks). Developed in 1960s, they have become the chief tools in analyzing effects of Global climatic change.CO2 doubling as one of the most important parameter affecting atmosphere was simulated using the resultant monthly indexes of temperature and precipitation on grid points in Tabriz for a 53-year time period (1952-2003). The resulting Hythergraph and Ambrothermic model of Geophysical Fluid Dynamics Laboratory (GDFL) for Tabriz indicate monthly increases of temperature and precipitation during the CO2 doubling periods. The temperature would increase monthly and seasonally, and the precipitation would decrease on March and increases on April and May. A comparison of the present and simulated Ambrothermic, Hyetograph and Xlimagram models applying GDFL model confirm precipitation and temperature changes in Tabriz. Therefore, the results verify climatic changes such as a decrement in the duration and intensity of cold season accompanying freezing days, and decreasing spring and winter precipitation and changing winter precipitation type from snow to rain, as well as, the extension of growth period, and finally the dominance of dry periods.